T cell receptor γ chain variable gene rearrangements in acute lymphoblastic leukemias of T and B lineage

The status of immunoglobulin and T cell receptor genes in acute lymphoblastic leukemia (ALL) of T and B lineage has been studied. Our data indicate that illegitimate gene rearrangements at immunoglobulin heavy chain (in T cell ALL), and T cell receptor β chain (in pre‐B ALL) genes are only rarely found (2 out of 30 patients). In contrast, T cell receptor γ chain gene rearrangements, characteristically found in T‐ALL, are also present in 7 of 18 patients with pre‐B ALL. Several features distinguish these illegitimate T cell receptor γ chain gene rearrangements from those in normal and leukemic T cells. Vγ genes located far upstream of the Jγ/Cγ complexes (Vγ2, Vγ3, Vγ4, Vγ5) appear to be preferentially used in normal adult peripheral blood T cells. In contrast, Vγ genes located immediately 5′ to the Jγ/Cγ complexes (Vγ8, Vγ9, Vγ10, Vγ11) predominate in Vγ‐Jγ recombinations observed in T‐ALL and pre‐B ALL. Whereas the Jγ2 region is primarily used in T cell receptor γ gene rearrangements observed in T‐ALL, those in pre‐B ALL are confined mostly to the Jγ1 region. These data suggest a limited accessibility of the T cell receptor γ chain gene locus for recombination processes in early stages of B cell differentiation.